The invention relates to a system for controlling at least one variable influencing the drive torque of an internal combustion engine of a motor vehicle.
Known wheel slip or drive torque control systems use slip or acceleration of the driven wheels as controlled variable. Throttle, ignition, fuel injection or wheel brake pressure are influenced by this controlled variable in a known way. Due to charge cycle processes and torsional stresses in the drive train between engine and driven wheels, when the throttle position is constant, for example, the drive torque and the engine speed are not constant and nor is the phase of the engine speed and speed of the driven wheels constant with respect to each other. Furthermore, a large time delay in the change of drive torque must be allowed for, in particular when modifying the throttle angle in spark-ignition engines.
For these reasons, very rapid, large system deviations may be produced by drive torque excess, which can lead to considerable losses in traction and lateral control force. Drive torque control systems are therefore extremely sensitive to excessive driving forces. Consequently, it is of great significance to keep the rate of rise and the excess of the drive torque small in the range in which the driven wheels enter the unstable range after exceeding the micro-slip curve.
In copending U.S. patent application Ser. No. 136,931, filed Dec. 23, 1987, a drive torque excess is modified by the drive torque being increased in portions at the instigation of the driver and, in the event of instabilities occurring when a wheel slip control is in operation, a further increase is inhibited. However, due to a time delay i.e., until the engine responds, for example, to a change in the throttle position, an undesirably high excess torque can still build up. to which the stresses in the drive train can also contribute.
Against this background, the object of the invention is to create a system for controlling the drive torque, by which undesirably high excess torques can be avoided.
This object is achieved according to the invention for spark-ignition engines and for diesel engines. Accordingly, as well as the controlled variable derived from the driven wheels, the engine speed is also used as additional input variable, in order to register the time delays of phase shifts between engine and driven wheels.
This is achieved in that, whenever a predetermined threshold value is exceeded by the controlled variable of a driven wheel, the drive torque is reduced to a value assigned to the engine speed at this instant, and additionally by a further component, which happens in different ways in spark-ignition and diesel engines. During the further course of the control process, the drive torque is then controlled according to a predetermined variation over time of the engine speed such that smallest possible system deviations and excess torques occur and thus a maximum of traction and lateral control force is achieved.
A further advantage of the control system according to the invention, incorporating the engine speed, in that, by modification of the ignition point or of the fuel injection quantity, the speed level can be modified very quickly and thus the controlled variable of the driven wheels can be modified rapidly.
This is of advantage in particular if the drive torque is to be adapted quickly, for example, when there is a sudden increase in the adhesion coefficient, in order to achieve optimum traction.
The exemplary embodiment relates to a motor vehicle with a carburetor engine.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.